#include <iostream>
using namespace std;
int kai (int);
int main ()
{
	int n;
	cin>>n;
	cout<<kai (n);
	return 0;
}
int kai (int s)
{
	if (s==1)
		return 0;
	else if (s==2)
		return 1;
	else
		return kai (s-1)+kai (s-2);
}
